In the last few years a high incidence of somatostatin receptors has been demonstrated in a variety of human ramors, e.g., pituitary tumors, neuroendocrine tumors, breast tumors, gastro-enteropancreatic tumors and their metastases. Some of them are small or slow-growing tarnors which are difficult to precisely localize by conventional diagnosis methods.
In vitro visualization of somatostain receptors has been performed through autoradiography of tumoral tissues using radioiodinated somatostatin analogues, e.g., [.sup.125 I-Tyr.sup.11 ] somatostatin-14 (Taylor, J. E. et al., Life Science (1988) 43:421) or [.sup.125 I-Tyr.sup.3 ]SMS 201-995 also called [.sup.125 I]204-090 (Reubi, J. C. et at., Brain Res. (1987) 406:891; Reubi, J. C. et al.,J. Clin. Endocr. Metab. (1987) 65:1127; Reubi, J. C. et al., Cancer Res. (1987) 47:551; Reubi, J. C. et al., Cancer Res. (1987) 47:5758).
Although some somatostatin peptides are useful in therapeutic or in vivo diagnostic applications, not all radioisotypes commonly employed in the medical community have been easy to chelate or label in it.